This invention relates to novel aromatic diamines containing olefinic groups and to photo-crosslinkable polyamic acids and polyimides made therefrom. In particular, it relates to aromatic diamines having pendant groups that contain at least two olefinic groups, and to soluble polyimides made therefrom for use in semiconductor fabrication.
Polyimides are used in the semiconductor industry as dielectric coatings on silicon chips. There are several processes by which polyimide coatings can be deposited on silicon chips. The conventional process is a multi-step process that employs a photoresist to mask the etching of a polyamic acid layer. The conventional process is illustrated in the drawing which will be hereinafter described.
A second process is described in U.S. Pat. No. 4,321,319. In the process of that patent, a solution of a photosensitive polyamic acid is formed from a dianhydride and a diamine that contains a photosensitive group. The solution, with a sensitizer present, is spread on a substrate and the solvent is evaporated to form a soluble polyamic acid coating. The coating is exposed to light through a mask which crosslinks the exposed portions of the coating, rendering them insoluble. The unexposed portions are then dissolved in a solvent and removed and the exposed portions are heated to close the imide ring and harden the film. This method must be used to form a pattern if the polyimide is insoluble and therefore a coating cannot be formed from a solution of the polyimide. This is a useful method, but when the imide ring is closed water is condensed out and its removal can leave voids, pinholes, or blisters in the coating.